Enphase Energy Inc (NASDAQ:ENPH) climbed +7.53% early in the day, its year-to-date gain now reaching +64.04%. Early in the month, the solar power solutions company announced two new partnership agreements, and its price has climbed a healthy +12.43% since then. Dan Loeb initiated a position in Enphase during the second quarter of 2012 and has gained over +50% on his original investment.

Taking the last spot on today’s list of midday gainers is Steel Dynamics, Inc. (NASDAQ:STLD), up +6.57% after announcing plans to buy a U.S. steel plant from Russian Severstal. In the investment portfolios of billionaire investors Jorge Lemann and Ray Dalio, Steel Dynamics has gained +30.21% over the past year.

Castlight Health Dips

Castlight Health Inc (NYSE:CSLT) fell -8.61%, rendering it today’s biggest midday loser. On Friday, the enterprise health care cloud company announced the expansion of its technology platform through an agreement with Teladoc, which apparently hasn’t enthused investors as much as hoped. Tiger Global initiated a position in Castlight in Q1 2014.

BioFuel Energy Corp. (NASDAQ:BIOF) dipped -6.38% midday, though enthusiasm surrounding the company continues. Just last week, Dan Loeb revealed a 19.3% beneficial interest in BIOF, which has climbed a staggering +380.12% since the start of the year.

Down -4.98%, Merrimack Pharmaceuticals Inc (NASDAQ:MACK) takes the third and final place on today’s list of midday losers. Short interest in the biotech firm declined in June, and analysts have commented on the stock recently as well (Brean Capital gave it a buy rating, and JPMorgan Chase & Co. overweight). Farallon Capital holds 317,000 MACK shares.